With the rapid improvement in performance of a computer system such as a mobile PC, a workstation, or a high-capacity server, high density recording of a magnetic disk device which is an external recoding device for such a computer system is being required. In order for high density recording of a magnetic disk device, it is necessary to reduce a distance between magnetic recording medium and a magnetic head-slider, reduce the size of grains constituting a magnetic film of the magnetic recoding medium, and enhance the coercivity of the magnetic recording medium. In the magnetic recording media, reducing the grain size causes noise reduction; however, a problem in which the grains become thermally unstable occurs. For this reason, in order to reduce the grain size and ensure thermal stability at the same time, it is necessary to increase the anisotropy field of a magnetic layer of the magnetic recording medium. This means that it is necessary to further increase a head magnetic field strength necessary for recording information. However, since there is a limit to the size of a magnetic head for recording, it becomes difficult to increase the anisotropy field, that is, to enhance the coercivity. As a result, high density recording becomes impossible.
In order to solve this, there has been proposed a thermally assisted recording method which heats magnetic recording medium with light only at a recording moment and uses near-field light to lower the coercivity of magnetic recording medium. The near-field light is an electromagnetic field localized in the vicinity of a micro object equal to or less than the wavelength of the light, and when light enters a metal object, plasmon resonance is excited in the metal object and strong near-field light is generated in the vicinity of a fore-end part of the metal object. In this case, the diameter of the irradiation spot of the near-field light is several tens of nm and thus it becomes possible to heat a part having the same size as the grain size of the magnetic recording medium. For this reason, in order to obtain a magnetic field sufficient for recording, a magnetic head for recording according to the prior art heats only a micro region to lower the coercivity, thereby making it possible to perform recording on magnetic recording media having high anisotropy field strength, that is, high coercivity for super-high density recording.
In general, a small-size low-power-consumption semiconductor laser is used as a light source from a point of view in which it is used in a magnetic disk device. In order to guide light from a semiconductor laser to a near-field light element, an optical component, for example, a reflective mirror, a lens, an optical fiber, an optical waveguide, etc., is used. However, since use of the above-mentioned optical component increases optical loss (hereinafter, referred to as coupling loss) in a coupling part, it is necessary to guide the light with as few components as possible. Reducing components is preferable because the length of a light path becomes short and thus loss due to attenuation is also reduced. Therefore, it is possible to minimize loss by disposing a semiconductor laser unit which is a light source in the vicinity of a magnetic head-slider.
As prior arts regarding thermally assisted recording in which a semiconductor laser unit is disposed in a magnetic head-slider as described above, there are techniques described in JP-A-2009-54205 and JP-A-2008-10026.
In JP-A-2009-54205, there is disclosed a method of guiding light to a near-field light element through an optical waveguide by disposing a semiconductor laser unit in a direction perpendicular to an air-bearing surface of a magnetic head-slider.
In JP-A-2008-10026, a semiconductor laser unit is disposed in a direction parallel with an air-bearing surface of a magnetic head-slider, the propagation direction of light is changed by 90 degrees with a diffractive optical element, and light is guided to a near-field light element through a refractive-index adjusting layer and an optical waveguide.
As described in JP-A-2009-54205, when a semiconductor laser unit is disposed on a magnetic head-slider side surface, since the semiconductor laser unit structurally becomes a cantilever structure, the semiconductor laser unit largely vibrates when the magnetic head-slider is flew on magnetic recoding medium. For this reason, relative misalignment between a light emitting opening of the semiconductor laser unit and a light receiving opening of an optical waveguide occurs. As a result, there is a problem in which coupling loss occurs. An increase in the coupling loss results in an increase in consumed power, which is a big problem.
Meanwhile, in the technique described in JP-A-2008-10026, a semiconductor laser unit not only generates light but also functions as a heat source. In particular, while driving a semiconductor laser, all of the current is converted into heat until a current value reaches an oscillation threshold value at which laser oscillation of the semiconductor laser unit starts such that the semiconductor laser unit produces heat by itself. In this prior art, countermeasures against heat are not mentioned. Further, as a material to adjust refractive index of this prior art, polymethylphenylsilane which is UV curable resin is used. This material is thermally decomposed by heat so as to generate contamination such as siloxne. This contamination is a material that inhibits flying in a magnetic disk device, and once contamination is generated, at the worst case scenario, probability in that a head crash occurs is high. As a result, there is a problem in which the reliability of the magnetic disk device is undermined.